Pipes used to carry liquids and gases commonly transport all types of materials including water, natural gas and liquid sewage. Over time, these pipes require servicing and cleaning. MacNeil et al. disclose an automated process for cleaning or restoring the inside of a pipe in U.S. Pat. No. 6,206,016. Macneil et al. use a single cleaning arm, which creates a helical cleaning pattern on a circular pipe. However, for pipes that deviate from a circular shape, the MacNeil process is limited, as the helical pattern is more difficult to maintain. Therefore, a device capable of more efficiently scarifying the interior surfaces of pipelines is desired.
The interior surface of a pipeline carrying solids, liquids and gases generally degrades over time as the pipe walls interact chemically and physically with the substances flowing through them and air. In particular, a sewer system's interior walls corrode and deteriorate because corrosive materials contaminate the surface, degrading the metal and concrete used to build the sewer pipe. The corrosive material arises from both the sewage and waste water itself, and also from the digestible by-products of bacteria found in the sewage which proliferate in the anaerobic environment. The corrosion causes the walls of the sewer pipe to physically decay, eventually reducing their overall thickness.
The principle source of corrosion is sulfuric acid, which arises as a product of the reaction of sewer gases with water and air in the sewer pipe and the sewer environment itself. Various metal sulfates found in the sewage quickly convert into hydrogen sulfide by reducing to sulfide ions in the waste water, combining with hydrogen in water and outgassing above the liquid as hydrogen sulfide gas. Additional hydrogen sulfide originates from bacteria-containing contaminants which accumulate on the relatively rough concrete below the maximum liquid level. Bacteria found in these accumulations thrive in the anaerobic sewer environment producing hydrogen sulfide gas as a respiratory by-product. Oxygen from the liquid below and oxygen condensing from the water in the air react with the hydrogen sulfide on the pipeline walls creating the highly corrosive sulfuric acid. The sulfuric acid attacks the calcium hydroxide in the concrete sewer walls leaving calcium sulfates which ultimately crumble and fall off the interior of the wall substantially reducing its thickness.
The waste water level varies over the course of a 24-hour period. The flow is at its lowest level between 1:00 a.m. and 6:00 a.m. in the morning but it rises distinctly in the daytime when the pipe may operate near capacity. Because of the gaseous nature of the hydrogen sulfide, the pipe walls are predominately corroded in the portions of the wall above the minimum liquid level. Portions of the walls which are always below the water level are not subjected to such high concentrations of hydrogen sulfide gas or sulfuric acid and consequently do not experience the same level of decay.
Eventually the sewer walls must be restored or they can suffer permanent damage leading to great expense. The restoration process is a two-step operation that consists of first scarifying the interior pipe surface to remove the contaminants (including any possibly existing outer layers of corrupted concrete) from the surface of the pipe, i.e. a process herein defined as scarifying, and then applying a protective coating over the newly cleaned (scarified) pipe surface. Attempting to apply a protective coating without first scarifying the pipe surface is futile because it does not stop the decay that has already begun underneath the coating. Furthermore, the protective coating itself does not adhere well to the contaminated surface. Thus, scarifying is an essential element of the restoration process.
As previously mentioned, the sewer typically operates at high capacity during the day with a decreased flow overnight. In order to restore the sewer pipes without diverting the flow (a costly and sometimes impossible alternative), a bulk of the work must be done at night during the brief period when the flow is at a minimum. As previously outlined, the restoration process involves both scarifying the pipe surface and applying a protective coat. In practice, the rate of restoration is impaired because manual scarifying takes a proportionally greater amount of time than does the application of the protective coat. Consequently, efficiency of the scarifying device is paramount to ensure that the maximum possible amount of work can be achieved during the minimum flow period. As multiple nights are typically required, it is also preferable to have a device that can be rapidly deployed to resume scarifying operations where they were left off the previous night.